This invention relates, in general, to semiconductor structures, and more particularly to a method of fabricating a semiconductor structure having self-aligned diffused junctions.
In an article entitled "A Novel CMOS Structure With a Reduced Drain-Substrate Capacitance", IEEE Transactions on Electron Devices, Vol. 36, No. 3, page 598, March 1989, Sagara et al. describe a CMOS structure and method of fabrication. To fabricate the structure, junctions are formed by the lateral diffusion of impurities from imbedded doped polysilicon films into mesas of the silicon substrate. The method employs no spacer technology. This method has relatively limited scalability because the total junction area is defined by a photolithographic etch and diffusion which require that lithographic parameters be maintained.
U.S. Pat. No. 4,569,701 entitled "Technique for Doping from a Polysilicon Transfer Layer" issued to Oh on Feb. 11, 1986 teaches that it is necessary to controllably dope trench sidewalls for trench isolation technology or trench capacitor type memory cells. The technique disclosed includes depositing a transfer layer of polysilicon to conformally coat the trench bottom, sidewalls and the top surface surrounding the trench An impurity is implanted into the polysilicon at the bottom of the trench and around the top surface. The impurity is diffused throughout the sidewalls by heating and may then be diffused into the substrate.
U.S. Pat. No. 4,209,350, entitled "Method for Forming Diffusions Having Narrow Dimensions Utilizing Reactive Ion Etching" issued to Ho et al. on June 24, 1980, is also related to the present invention. Diffusions having submicrometer dimensions are formed in a silicon body by forming insulator regions having substantially horizontal and vertical surfaces and then forming a layer having a desired dopant concentration thereon. The layer is then reactive ion etched to remove only the horizontally disposed portions of the layer. The dopant is then diffused into the silicon body by heating.
Accordingly, it would be highly desirable to fabricate a structure having self-aligned diffused junctions that are highly scaleable, not defined by photolithographic parameters and includes integrated contacts through a horizontal semiconductor layer.